netdev - RE: [PATCH 2.6.32 3/3] net: Make ks8851 snl work under Beagle Zippy combo board

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Date:	Mon, 21 Dec 2009 14:07:14 -0800
From:	"Ha, Tristram" <Tristram.Ha@...rel.Com>
To:	"David Miller" <davem@...emloft.net>
Cc:	<ben@...tec.co.uk>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2.6.32 3/3] net: Make ks8851 snl work under Beagle Zippy combo board

Ha, Tristram wrote:
> David Miller wrote:
>> 
>> You say "may not be necessary", do you actually know for sure?
>> 
>> This seems questionable, if the interrupt disabling was there for a
>> reason what has changed to make it such that it is no longer
necessary?
> 
> I have tested the KSZ8851 SNL driver using the OMAP Beagle Zippy combo
board, developed by Tin
> Can Tools.  Ben Dooks, who implemented the original driver, has his
own KSZ8851 SNL evaluation
> board, but he probably did not run any performance test on the driver.
I did sent him the
> changes before so that he can verify on his board, but I have not
received any response.   
> 
> So I really do not know if interrupt disabling is necessary or not.
But from my understanding
> of the SPI network driver model, it is almost required the interrupt
be edge triggered, as the
> hardware interrupt cannot be disabled inside the actual interrupt
handling routine.  So if the
> interrupt is level triggered, the interrupt routine will be called
continually, and there is no
> chance for the workqueue to disable the interrupt.  As the interrupt
is edge triggered, I do not
> think the interrupt needs to be disabled.     

The "[PATCH 2.6.33] net: Fix ks8851 snl receive problem" I just
submitted turns off hardware interrupt during interrupt handling.  That
makes the disable_irq() call really unnecessary when the interrupt is
edge-triggered.  The code also works when the interrupt is
level-triggered under Beagle Zippy combo board, but theoretically the
disable_irq() is required when the interrupt is level-triggered.  When I
first worked on the ks8851 driver I was using Linux 2.6.22, and the
level-triggered interrupt code did not work.  That is why I changed the
code to edge-triggered.
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